Pesticides to Kill Grub Worms

Grubs enjoy your lawn as much as you do.

Grubs are common grass pests that destroy large sections of lawn if allowed to go unchecked. The most common of these pests is the white grub, also called a grubworm, which includes the larvae of Japanese beetles, June beetles, masked chafers and other beetles. They can be controlled with good lawn management as well as the application of specific pesticides.

Verification

Authorities at the University of California Integrated Pest Management (IPM) Program suggest checking carefully to ensure white grubs actually are present before trying to kill them. What looks like grub damage may be dog urine spots, for example, or the result of the wrong type of grass for a yard, improper watering and some fertilizers. Dig into the ground to see the roots of your lawn. If you find more than five or six white grubs per 1 square foot, your yard should be treated for grubs.

Pesticides

Apply imidacloprid to your lawn to kill young grubs, though it’s not generally effective against larger grubs. Halofenozide is a growth inhibitor that also kills young grubs but only in the early stages of their development. Both pesticides stay in the soil for an extended period of time, and so they can be applied in advance to lawns with a history of grub problems. Because carbaryl and pyrethroids are harmful to beneficial insects and can pollute the water supply, the University of California IPM Program recommends not using either of them.

Alternatives

It’s possible to cut the number of grubs in your lawn in half by applying beneficial nematodes, tiny worms that attack insects. Purchase and release at least 1 billion Heterorhabditis bacteriophora nematodes per 1 acre of lawn or 2 billion Steinernema glaseri nematodes for 1 acre of lawn. Another effective biological control that doesn’t pollute the environment is Bacillus popilliae, milky spore disease, a bacteria that attacks and kills Japanese beetle larvae and some other kinds of grubs.

Environmental Changes

Make your yard unfriendly to grubworms by watering it deeply but not often. Aerate the lawn at least once each year, and rake out all the thatch that is more than 1/2 inch deep. Grass shouldn't be cut too short; no more than the top one-third of grass should be removed during a single mowing. Using chemicals such as fertilizer, pesticides and herbicides carefully and applying each per its manufacturer’s instructions can reduce the chances of factors other than grubs causing brown spots in grass. Don’t allow your dog to relieve itself on your lawn. If the lawn has thin spots, cover them in fall and spring with grass seed suited for the yard's conditions.